1. Field of the Invention
The present invention relates to a system for the detection of objects on a display screen and, more particularly, to a system for detecting objects on a display screen using an external detection pointing device.
2. State of the Art
Typically, graphical display systems include a display screen having an associated cathode-ray tube (CRT) in which an electron beam is scanned across a photosensitive layer of material, such as phosphorous, to cause an image to be displayed on the screen. The image can include a collection of objects or can be textual. The electron beam, and hence, the image is typically controlled by a CRT and graphics controller. Often, such systems include a human interface device which allows a system user to interact with the information being displayed on the screen. In particular, one specific type of user interface is one in which the user aims at the screen and the location at which the interface is aimed is determined by the graphics or CRT controller.
One example of a graphical display system having the above-described type of user interface is a video game system. Typically, a video game displays moving objects on a screen. The user interface is often embodied as a pointing or aiming device such as an arcade gun having a trigger. In use, a user aims the detector at objects on the screen and depresses the trigger. If the detector is aligned with the position of one of the objects on the screen a "hit" is achieved, if not a "miss" occurs. Hence in this type of system, the graphical display system operates as if it recognizes whether the detector is pointing at a given object on the display screen.
One manner in which such apparent "point on shoot" operation is achieved is by using a CRT row/column counter that tracks the location of the electron beam on the screen the CRT beam is scanning. While aiming the device at the screen, the user transmits a pulse to the display system CRT or graphics controller (e.g., by pulling the trigger of an arcade gun) which causes the most current row/column values of the counter to be latched. These values represent where the detector was pointed when the trigger was depressed. In this system, the connection between the detector and the row/column circuitry is a relatively fast communication path (typically, directly wired) and hence, by the time the pulse is transmitted from the detector to the row/column circuitry, the difference between the actual location of the detector and the latched row/column location is relatively small. Hence, the accuracy of this detection technique relies on a fast communication path between the detector device and the row/column circuitry.
Recently graphical display systems are being designed such that the connection between the user interface (i.e. the aiming detector device) and the display system is a software controlled interface. Specifically, the connection can be embodied as a polled interface in which the user interface cannot initiate a communication with the host system (i.e. the graphics or system controller) on its own. Instead, it is first polled by the host system. Hence, with respect to the above object detection system, the host system would need to poll the detector device prior to the detector device providing the pulse to the row/column circuitry to latch its location. However, since this communication process can take a relatively long time, object detection accuracy is greatly diminished using the above technique which relies on a "fast" path between the detecting device and the CRT control circuitry.
What is needed is a system and method for detecting objects on a display screen which is not constrained by the speed of the communication path between the aiming detector device and the display system controller.